Proceedixgs of the P olttechnic Association. 889 



the bottom of the atmospheric ocean and form a layer five feet in 

 depth. But, if only the normal amount be present, it is completely 

 diffused, so that we find it existing in exactly the same proportion on 

 tlie mountain and in the valley. But, if more than 1-2500 be present, 

 the tendency is to settle at the bottom, making the per cent of car- 

 bonic acid greater near tlie surface than in the higher regions. Thus, 

 in the Grotto del Cane, in Italy, where the gas escapes in large quan- 

 tities from the earth, all animals entering tlie cave almost instantly 

 die from the effect of breathing the carbonic acid. Now, if the air 

 contain only one or two per cent, its effect is clearly poisonous. If 

 ten per cent, it produces immediate death. 



Heat and Yentilation. 



We have attempted to demonstrate that pure air is the normal 

 breath of man ; but art and civilization have induced conditions which 

 to a greater or less extent interfere with or antagonize the purely 

 normal conditions. 



Man finds that it is necessary to his comfort to be sheltered from 

 tlie heat and rain of the tropics, aiid from the heat and cold and storms 

 of the temperate and frigid regions. To accomplish this end, he erects 

 the roof and builds the wall about him ; in short, he buihls a house. 



Now, this house is an evidence of high civilization ; it adds to his 

 comfort. But by living beneath this roof, within these walls he has, 

 to a certain extent, disregarded the normal conditions, for the ai^ 

 within the confined space is not so pure as that which surrounds it, 

 and, therefore, liis respiration is imperfect. Again, in all the regions 

 of tlie earth north of twenty-five degrees south latitude, and south of 

 twenty-five degrees north latitude, man finds that artificial heat is 

 necessary, and in our latitude is required in our houses for more than 

 half the year. Plere, then, is another artificial condition, and one 

 which, to a greater or less extent, interferes with the natural or nor- 

 mal condition. If the fire l^e made to burn in an open fire place, or 

 in a close stove, a portion of the oxygen of the air is required to 

 oxydize the fuel. Now, if the supply from without be suificient, both 

 for respiration and combustion, little heat could be imparted to the 

 room ; because the supply must be of the same temperature as that 

 of the air outside the house. On the other hand, if we cut off the 

 full supply, the air in the house might be warmed, but would be 

 rendered impure. In short, the air would be as we find it in nearly 

 all our houses — hot, but poisonous. No doubt that either the old 



